research article differences in swallowing between high...

Research ArticleDifferences in Swallowing between High andLow Concentration Taste Stimuli

Ahmed Nagy,1,2 Catriona M. Steele,1,3,4 and Cathy A. Pelletier5,6

1 Toronto Rehabilitation Institute, University Health Network, 550 University Avenue, No. 12-101, Toronto, ON, Canada M5G 2A22University of Fayoum, Fayoum 63514, Egypt3 University of Toronto, Toronto, ON, Canada M5V 1G74Bloorview Research Institute, Toronto, ON, Canada M4G 1R85University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA6Charlestown Retirement Community, Catonsville, MD 21228, USA

Correspondence should be addressed to Catriona M. Steele; [email protected]

Received 16 January 2014; Revised 22 February 2014; Accepted 10 April 2014; Published 30 April 2014

Academic Editor: Alberto Raggi

Copyright © 2014 Ahmed Nagy et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Taste is a property that is thought to potentially modulate swallowing behavior. Whether such effects depend on taste, intensityremains unclear. This study explored differences in the amplitudes of tongue-palate pressures in swallowing as a function oftaste stimulus concentration. Tongue-palate pressures were collected in 80 healthy women, in two age groups (under 40, over60), stratified by genetic taste status (nontasters, supertasters). Liquids with different taste qualities (sweet, sour, salty, and bitter)were presented in high and low concentrations. General labeled magnitude scale ratings captured perceived taste intensity andliking/disliking of the test liquids. Path analysis explored whether factors of taste, concentration, age group, and/or genetic tastestatus impacted: (1) perceived intensity; (2) palatability; and (3) swallowing pressures. Higher ratings of perceived intensity werefound in supertasters andwith higher concentrations, whichweremore liked/disliked than lower concentrations. Sweet stimuli weremore palatable than sour, salty, or bitter stimuli. Higher concentrations elicited stronger tongue-palate pressures independently andin association with intensity ratings. The perceived intensity of a taste stimulus varies as a function of stimulus concentration, tastequality, participant age, and genetic taste status and influences swallowing pressure amplitudes. High-concentration salty and sourstimuli elicit the greatest tongue-palate pressures.

1. Introduction

The influence of taste on swallowing behavior is not wellunderstood, although several studies in the literature pointto the possibility that particular taste stimuli may have thepotential to improve swallowing function in individuals withdysphagia. To date, sour tasting stimuli such as lemon juice orcitric acid solutions have been most frequently studied [1–7].A critical question arising from these studies is whether theinfluence of taste on swallowing is concentration dependent[2]. A study by Pelletier and Lawless [2] found that a high-concentration (2.7% w/v) sour citric acid solution reducedpenetration aspiration in older adults undergoing endoscopicexamination of swallowing, but lower-concentration sourand sweet-sour stimuli did not have this effect. The authorsinterpreted these results to suggest that high-concentration

sour stimuli might activate trigeminal nerve afferent recep-tors and influence swallowing via a phenomenon calledchemesthesis [2].

Very few studies have investigated the impact of vary-ing stimulus concentration on swallowing physiology. In astudy on rats by Kajii and colleagues [8], the efficiency ofreflex swallow initiation after applying sour and other tastesolutions to the pharyngolaryngeal mucosa was investigated.Acetic and citric acids, both of which are sour, showedthe highest efficiency in eliciting the reflex swallow, andthis efficiency increased at higher stimulus concentrations.These data have been interpreted to suggest that higher-concentration sour stimuli may alter response thresholds atthe oropharyngeal receptor level, yielding heightened stim-ulation of swallowing trigger neurons in the nucleus tractussolitarius, which in turn facilitate heightened activation

Hindawi Publishing CorporationBioMed Research InternationalVolume 2014, Article ID 813084, 12 pageshttp://dx.doi.org/10.1155/2014/813084

2 BioMed Research International

of swallowing motor neurons via the nucleus ambiguus,ultimately resulting in more efficient swallowing [2]. In anelectromyography study by Palmer and colleagues [5], sourlemon juice stimuli were shown to elicit stronger contractionof the suprahyoid musculature, as well as a muscle con-traction pattern that was more tightly concatenated acrossthe onsets of the mylohyoid, geniohyoid, and anterior bellydigastric muscles compared to water. Thus, taste appears topossibly modulate both the timing and strength of swallow-ing.

High-concentration stimuli are usually perceived to be ofgreater intensity than lower concentrations of the same stim-uli [9]. However, the perceived intensity for a given stimulusmay differ across individuals, based on factors including priorexperience, age, gender, disease, and (in the case of taste per-ception) genetic taste status [10]. Taste sensitivity is known tovary across the population based on genetic histoanatomicaldifferences on chromosome 7: individuals with two recessivealleles of the taste gene are nontasters, those who have adominant and recessive combination are medium tasters,and those with two dominant alleles are genetic supertasters.Supertasters are known to report heightened perception ofbitterness when tasting 6n-propylthiouracil (PROP), and thedegree of bitterness perceived is reported to be proportionalto the density of fungiform papillae on the tongue [11].

The perceived intensity of a stimulus differs from itspalatability, which reflects personal preference on the partof the person exposed to the stimulus. Only one study hasexplored the relationship between taste stimulus palatabilityand swallowing behaviors, measured in the form of tongue-palate pressures [3] and found no effect. More recently,Dietsch and colleagues [12] have shown that the addition ofbarium to taste stimuli lowers both their perceived intensityand palatability, with these effects being seen more stronglyin older participants and in supertasters. Thus, the incorpo-ration of both palatability and perceived intensity measureswhen studying the influence of taste and taste concentrationon swallowing is warranted. This was the goal of the currentstudy, which forms part of a larger project known as theArkansas Taste and Swallowing Study (ARTSS). Specifically,the analysis described in this paper sought to answer thefollowing questions using a sample of healthy adult womenwith divergent age profiles and genetic taste status and tastestimuli with four perceptual taste qualities (sweet, sour, bitter,and salty), each serving in two concentrations (high, low).

(1a) Does perceived taste intensity vary as a function oftaste quality, stimulus concentration, age group, and/or genetic tasting status?

For this question, we hypothesized that greater perceivedtaste intensity would be reported by all participants for higherstimulus concentrations and that supertasters would reporthigher perceived taste intensity than nontasters.

(1b) Do palatability ratings vary as a function of taste qual-ity, stimulus concentration, age group, and/or genetictasting status?

We expected that the low-concentration stimuli would berated as more palatable than high-concentration stimuli by

all participants and that the sweet stimuli would be preferred(i.e., rated as more palatable) than the sour, salty, and bitterstimuli. We also expected to see an effect of genetic tastestatus, such that palatability ratings would be more extreme(i.e., greater like/dislike) in supertasters.

(2) Do strength-normalizedmeasures of anterior tongue-palate swallowing pressure vary as a function of tastequality, stimulus concentration, age group, and/orgenetic taste status?

Our hypotheses were that stronger amplitudes of tongue-palate pressure would be seen for the sour stimuli comparedto the other taste qualities and also for the high-concentrationstimuli in comparison to the low concentration stimuli.

(3a) Does perceived taste intensity modulate the effectsseen in question 3?

(3b) Does palatability modulate the effects seen in ques-tion 3?

With respect to the predicted modulatory effects of palatabil-ity and perceived intensity on tongue-palate pressure varia-tion, we adopted the null hypothesis, expecting no modula-tory effects of palatability or perceived intensity on tongue-pressure amplitudes. However, should modulatory effects beidentified, we would expect to see greater modulation insupertasters given the predictions of higher taste intensityratings and more extreme palatability ratings in supertasters.

2. Methods

The methods of the ARTSS study have been reported else-where [13] but will be briefly summarized below.

2.1. Participants. A sample of 80 healthy community dwellingwomen was recruited, stratified by genetic taste status, basedon their bitterness ratings (≤20 versus ≥50) of a PROP filterpaper using the general labeled magnitude scale (gLMS) [14].The study sample was limited to women given that femalesare known to be more likely to classify at the extremes ofthe genetic taste distribution than males [15]. Genetic tastestatus was equally distributed (20 supertasters, 20 nontasters)in each of two age cohorts (young: <40; mature: ≥60 yearsof age). Participant demographics are summarized in Table 1.All participants were deemed to have adequate cognitiveability to participate based on a score of at least 25 on theminimental state examination [16]. A total of 222 womenwere screened for inclusion in order to accrue the desiredsample size with the planned stratification of genetic tastestatus within age group.

2.2. Stimuli. Pure taste stimuli (i.e., without aroma) wereprepared in deionized water (Millipore 60 LiterProgrardTMTank), with paired concentrations (high and low) for eachof four taste qualities (sweet, sour, bitter, and salty). Table 2lists the chemicals used and their molar concentrations foreach stimulus. Additional water, barium, ethanol, and car-bonated stimuli were also part of the protocol [12, 17] but

BioMed Research International 3

Table 1: Participant demographics.

Genetic taste status Age group 𝑁 Mean Age (years) Standarddeviation

Nontasters Young (<40) 20 25.8 4.7Mature (>60) 20 71.5 8.7

Supertasters Young (<40) 20 26.5 3.4Mature (>60) 20 72.6 7.4

Table 2: Liquid stimuli used in the study.

Taste quality Chemical Stimulus concentration Molar concentration

Sweet Sucrose (table sugar) High (+) 1MLow (−) 0.15M

Sour Citric acid USP∗ High (+) 0.128MLow (−) 0.002M

Salty Sodium chloride USP∗ High (+) 1MLow (−) 0.034M

Bitter Anhydrous caffeine USP∗ High (+) 0.032MLow (−) 0.003M

∗All chemicals were obtained from http://www.sciencelab.com/.

were only presented at single concentrations and are thereforenot included in the analysis discussed in this paper. Giventhat the focus of this paper is on the influence of perceptualcharacteristics of the taste stimuli (intensity and palatability),we adopt the convention of referring to the stimuli by theirtaste qualities rather than their chemical compositions.

2.3. Protocol. Stimulus sets of chilled 5mL samples of eachtest liquid were prepared in clear cups and arranged in a ran-dom order. All samples were kept in a refrigerator until pre-sentation. Tongue-pressure sensors were applied (describedbelow), together with a nasal cannula (to record airflowdirection) and submental surface electromyography sensors.When the participants had acclimatized to the sensors(approximately 5 minutes), each randomized sample wasswallowed and rated for taste intensity using the gLMS [14].Participants were blinded to the content of each stimulusprior to sampling, and 3 or more oral rinses with room-temperature tap water were used after each sample until theparticipant confirmed that they no longer had any residualperception of taste ormouthfeel. After completion of the tasteintensity ratings for the entire stimulus set, the sensors wereremoved and a 15–30 minute break was taken before pro-ceeding with the second part of the experiment. Participantsremained in the data collection room throughout the breakand were not allowed to eat or drink during that time. For thesecond part of the experiment, participants swallowed eachrandomized sample again, with postsample rinses employedas previously described to remove residual taste ormouthfeel.Palatability ratings (i.e., degree of like/dislike) were capturedusing a hedonic version of the gLMS (H-gLMS) [18]. The H-gLMS resembles two mirrored and stacked gLMS scales suchthat the range is −100 to +100, reflecting a range from intensedislike to intense like.

2.4. Tongue-Palate Pressure Measurement. In order to mon-itor swallowing function, three types of data (respiratory,tongue-palate pressure, and submental electromyography)were collected using the KayPENTAXDigital SwallowWork-station (Montvale, NJ). Only the tongue-palate pressurewill be discussed here. The three-bulb lingua-palatal sensorarray provided with the KayPENTAX Swallowing SignalsLab was adapted for the study by removing one bulb fromthe pressure sensor strip; this was done to avoid a biasedsample population given experience that female participantswith smaller mouths frequently gag with the full-length strip[3]. The shorter two-bulb sensor strip was secured witha medical adhesive (Stomahesive, Convatec, St. Laurent,Quebec) to the roof of themouth inmidline, with the anteriorbulb positioned immediately behind the upper teeth. Givenprevious evidence that data registered at the mid palate arehighly volatile [19], perhaps due to variations in palatal vaultheight across participants, the current analysis is restricted todata collected at the anterior palate. Pressures were measuredcontinuously within a range of 0–500mmHg at 250Hz.Time was allowed for acclimatization to the sensors prior tobeginning swallowing tasks.

2.5. Data Processing. The anterior palate pressure bulb signalwas indexed using the KayPENTAX DSW software cursorfunction to find and extract amplitudemeasures of the onsetsand peaks of pressure for each swallow in the protocol. Beforeproceeding further, we explored the possibility that measuresof tongue pressure amplitude in this data set might varyaccording to differences tongue strength across participants.Pearson’s correlations between the swallowing pressure dataand a reference measure of each participant’s peak amplitudecollected during an effortful saliva swallow task showed arelationship of r = 0.38, P = 0.000. Linear regression showed


R = 0.38, P = 0.000

R2 linear = 0.142

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Figure 1: Relationship between tongue-palate pressures observedduring liquid swallowing tasks and participant strength, measuredas peak tongue-palate pressure during an effortful saliva swallowingtask.

Palatability

Tongue pressures in swallowing

(normalized to effortful saliva swallow range)

Q1a

Q1b

Q2

Q3a

Q3b

Taste quality

Genetic taste status

Age group

Stimulus concentration

Perceived taste intensity

Figure 2: Diagram illustrating the path analysis used in this study.

that 14.2% of the variability in swallowing pressure ampli-tudes was explained by variations in amplitude on theeffortful saliva swallow task (Figure 1). Therefore, we decidedto transform all swallowing pressure amplitude measures tostrength-normalized values, expressing them as a percent ofthe effortful saliva swallow strength reference [20].

3. Analysis

3.1. Statistics. Path analysis (see Figure 2) was used [21] toaddress the questions in this study. Path analysis is a well-established statistical approach in which a stepwise series ofANOVAs are performed to test components before building afinal AN(C)OVA model. Path analysis begins with the initialassumption that there may be modulatory effects of covariatefactors on the patterns of variation seen in a dependent

variable. The approach first tests whether these potentialcovariates vary as a function of the main factors in the model(in this case, questions (1a) and (1b), exploring whether tasteintensity or palatability varies as a function of taste quality,stimulus concentration, genetic taste status, and age group).Based on the results of these preliminary explorations, theargument for exploring the influence of these potentialcovariates on the main dependent variable at a later stagein the analysis (questions (3a) and (3b)) is either supportedor refuted. Question (2) in our paper describes the primarystudy question (differences in tongue-pressure amplitudes asa function of taste quality, stimulus concentration, genetictaste status, and age group) without consideration of thecovariates. The final step in the model refines question (2)model by integrating significant factors from questions (1a)and (1b) as covariates (in this case, questions (3a) and (3b)).Each step in this process involved fully factorialmixed-modelanalyses of variance with a compound symmetry structure,which was determined to have the best fit with the databased on restricted log likelihood estimation. For questions(1a), (1b), and (2) these were 4-way ANOVAs with within-participant factors of taste quality and stimulus concentrationand between-participant factors of genetic taste status and agegroup. For questions (3a) and (3b), the modulatory effectsof taste intensity and palatability were explored separately byadding these factors as covariates into the statistical model(ANCOVA). For all analyses, an a priori alpha criterion forstatistical significance was established at 𝑃 < 0.05. Significanteffects and interactions were further explored using Sidaktests for pairwise comparisons, with the strength of thesepairwise significant differences being further characterizedusing Cohen’s dmeasures of effect size (0.2–0.5 = small; 0.5–0.8 = medium; >0.8 = strong) [22].

4. Results

4.1. Question (1a) (Taste Intensity). Table 3 provides descrip-tive statistics for the perceptual ratings of taste intensityby taste quality, stimulus concentration, age group, andgenetic taste status. Several 2-way interactions were foundto be significant: age group X stimulus concentration (F(1,454.15) = 4.215, P = 0.041), genetic taste status X stimulusconcentration (F(1, 454.15) = 17.639, P = 0.000), and tastequality X stimulus concentration (F(3, 451.18) = 9.096, P =0.000). Additionally, statistically significant main effects werefound for stimulus concentration (F(1, 454.15) = 918.117, P =0.000, Cohen’s d = 1.38, i.e., large), and genetic taste status(F(1, 74.75) =13.278, P = 0.000, Cohen’s d = 0.41, i.e., small).These results can be summarized as showing that ratings ofgreater perceived intensity were triggered by higher stim-ulus concentrations and that supertasters reported greaterperceived intensity than nontasters. These findings providejustification for exploring the modulatory effects of tasteintensity at a later stage in the analysis process (question(3a)). The results for question (1a) are illustrated in Figure 3with the low and high concentrations of each taste qualitymarked by (−) and (+) diacritics, respectively. As shown inthe figure, the interactions of stimulus concentration, agegroup, and genetic taste status reveal a heightened degree


Table 3: Descriptive statistics for gLMS ratings of perceived intensity, shown by taste quality, stimulus concentration, participant age group,and genetic taste status.

Taste quality/stimulusconcentration Age group/genetic taste status Mean 95% confidence interval Standard deviation

Lower boundary Upper boundary

Salty (−)

Young nontaster 6.44 3.18 9.71 6.57Young supertaster 14.06 3.17 24.94 21.89Mature nontaster 7.44 4.32 10.57 4.07Mature supertaster 9.30 5.24 13.36 5.68

Sour (−)


Sweet (−)


Bitter (−)


Sweet (+)


Bitter (+)


Sour (+)


Salty (+)


of increase in perceived intensity for the high concentrationstimuli in the older participants (Cohen’s d = 0.36, i.e., small)and in supertasters (Cohen’s d = 0.61, i.e., medium). Effectsize measures for the concentration comparison were largefor all four taste qualities with weaker contrasts seen for thesweet (d = 1.13) and bitter stimuli (d = 1.16) than for the sour(d = 1.57) and salty (d = 1.66) stimuli. Interestingly, the low-and high-concentration salty stimuli accounted for both thelowest and highest reported intensity ratings and thus formedthe boundary conditions across all stimuli tested.

4.2. Question (1b) (Palatability). Table 4 shows descriptivestatistics for ratings of palatability by taste quality, stimulus

concentration, age group, and genetic taste status. In general,it can be noted that each taste quality was either liked(sweet) or disliked (sour, salty, or bitter), and the degreeof liking or disliking was dependent on perceived intensity.Explorations of this relationship using Pearson’s correlationsand absolute values of the palatability ratings (i.e., removingthe polarity) showed a correlation of r = 0.63 (P = 0.000)with perceived intensity. Several significant results supportthe plan to explore the modulatory effects of palatability inquestion (3b) of the analysis.

Two different 3-way interactions proved significant forthe palatability parameter. First, stimulus concentrationshowed a significant 3-way interaction with age group and


Table 4: Descriptive statistics for H-gLMS ratings of palatability, shown by taste quality, stimulus concentration, participant age group, andgenetic taste status.

Taste quality/stimulusconcentration Age group/genetic taste status Mean 95% confidence interval Standard deviation


Bitter (+)

Young nontaster −28.89 −39.16 −18.62 20.66Young supertaster −61.40 −76.86 −45.94 27.91Mature nontaster −42.00 −56.03 −27.97 24.30Mature supertaster −62.35 −76.73 −47.98 27.96

Sour (+)

Young nontaster −12.70 −31.94 6.54 41.11Young supertaster −22.00 −41.86 −2.14 41.20Mature nontaster −53.32 −70.33 −36.30 35.30Mature supertaster −48.22 −62.50 −33.94 28.71

Salty (+)


Bitter (−)


Salty (−)

Young nontaster −3.44 −9.04 2.15 11.25Young supertaster −11.67 −19.93 −3.40 16.62Mature nontaster −5.88 −13.69 1.94 14.67Mature supertaster −1.45 −8.41 5.51 14.87

Sour (−)

Young nontaster −5.11 −11.47 1.25 12.78Young supertaster −2.94 −14.59 8.70 23.42Mature nontaster 0.50 −8.94 9.94 17.72Mature supertaster −5.15 −10.45 0.15 11.32

Sweet (−)


Sweet (+)


taste quality (F(3, 467.60) = 3.122, P = 0.026), building onsignificant 2-way interactions between stimulus concentra-tion X age group (F(1, 468.4) = 10.104, P = 0.002), stimulusconcentration X taste quality (F(3, 467.60) = 30, P = 0.000),and age group X taste quality (F(3, 468.15) = 3.27, P = 0.021).Second, a significant taste quality X age group X genetictaste status interaction was seen (F(3, 468.145) = 4.726, P =0.003), building on the previously reported significant 2-waytaste quality X age-group interaction. To understand theseinteractions, it is important first to dissect their componentsin terms of significant main effects. Statistically significantdifferences in palatability were found between the differenttaste qualities (F(3, 468) = 146.43, P = 0.000), with the bitter

stimuli being significantly more disliked than the sweetstimuli (Cohen’s d = 1.55, i.e., large) and also more dislikedthan the salty and sour stimuli (d = 0.33 to 0.34, i.e., small).In addition to being markedly preferred over the bitterstimuli, the sweet stimuli were also significantly more likedthan the salty and sour stimuli (Cohen’s d = 1.2, i.e., large).Significant differences in palatability were also found as afactor of stimulus concentration: high-concentration stimuliwere liked/disliked significantlymore than the correspondinglow-concentration stimuli ((F(1, 468) = 88.17, P = 0.000,Cohen’s d = 0.53, i.e., medium). Furthermore, supertastersreported more extreme like/dislike than nontasters (F(1,68.13) = 6.22, P = 0.015, Cohen’s d = 0.19, i.e., small).


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Figure 3:Three-way interaction observed for ratings of perceived intensity between stimuli with four taste qualities as a function of stimulusconcentration and participant age group.

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Figure 4: Three-way interaction observed for palatability ratings of liquid stimuli as a function of taste quality, stimulus concentration, andparticipant age group.

The combined results arising from the interactions ofstimulus concentration, age group, and taste quality areillustrated in Figure 4 and can be summarized as showing thestrongest liking for the high-concentration sweet stimulus,the greatest dislike for the high concentration bitter stimulus,and a difference between younger and older participants withrespect to whether the high-concentration sour was moredisliked than the high-concentration salty stimulus (or vice

versa). The low concentration sweet stimulus was more likedthan the other three low-concentration stimuli, for whichpalatability ratings were in the mild dislike range, close tothe neutral zero value. Similarly, the combined effect arisingfrom the interaction of taste quality X age group X genetictaste status interaction is illustrated in Figure 5, which showsoverall liking for the sweet taste quality and disliking for theother three tastes (of which the bitter was most disliked).


Table 5: Descriptive statistics for strength-normalized measures of anterior tongue-palate swallowing pressures (in % of effortful salivaswallow amplitudes), shown by taste quality, stimulus concentration, participant age group, and genetic taste status.

Taste quality/stimulusconcentration Age group/genetic taste status Mean 95% Confidence interval Standard deviation


Sweet (−)


Sour (−)


Bitter (−)


Salty (−)


Salty (+)


Bitter (+)


Sweet (+)


Sour (+)


Among the supertasters, the mature participants showed lessdislike for the bitter and sour stimuli and less liking ofthe sweet stimuli than the younger participants but greaterdisliking of the salty stimulus. Among the nontasters, themature participants showed more extreme liking or dislikingfor all four tastes than the younger participants.

4.3. Question (2) (Tongue Pressure Amplitudes). Table 5 pro-vides descriptive statistics for the strength-normalized valuesof anterior tongue-palate swallow pressure amplitude. Asignificant 3-way taste quality X stimulus concentration Xgenetic taste status interaction was found (F(3, 476) = 3.77,P = 0.011) together with a significant 2-way taste qualityX stimulus concentration interaction (F(3, 476) = 2.76,

P = 0.04). Additionally, a significant main effect of stimulusconcentration was found (F(1, 476) = 13.48, P = 0.000)but with only a negligible effect size (Cohen’s d = 0.17),showing larger amplitudes of tongue pressure for higher-concentration stimuli. The 3-way interaction is illustrated inFigure 6, showing a general pattern of stronger tongue-palatepressures for higher-concentration stimuli in the supertastergroup. A marked increase in pressure amplitude is also seenfor the high-concentration salty stimulus compared to its lowconcentration comparator amongst nontasters.

4.4. Question (3) (Modulation of Tongue Pressure Variationrelated to Taste Intensity and Palatability). Given the resultsof questions (1a), (1b), and (2), continued explorations of


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Bitter Salty Sour SweetTaste quality

Young nontasterYoung supertaster

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Figure 5: Three-way interaction observed for ratings of palatabilityfor liquid stimuli as a function of taste quality, participant age group,and genetic taste status.

the statistical model incorporating covariate effects of per-ceived intensity and palatability were warranted. The modelwas simplified to remove age group as a factor given theabsence of age-group differences (or interactions involvingage-group contrasts) in strength-normalized measures ofanterior tongue-palate pressure amplitudes in question (2).

The incorporation of perceived intensity into the modelas a covariate (i.e., question (3a)) yielded a single significantfinding in the form of a significant 3-way interaction betweentaste quality, stimulus concentration, and genetic taste status(F(3, 403.91) = 3.44, P = 0.017). It is noted that this findingmatches the 3-way interaction pattern observed previously inquestion (2). Intensity by itself did not show significance as afactor.

The incorporation of palatability ratings into the modelas a covariate (i.e., question (3b)) yielded a single signif-icant main effect of stimulus concentration on strength-normalized measures of tongue-palate pressure amplitude(F(1, 413) = 12.271, P = 0.001) with stronger pressures gen-erated for higher-concentration stimuli. This finding alsomatches the results seen previously in question (2). Palata-bility by itself did not show significant influence.

5. Discussion

This study explores variations in tongue pressure amplitudesduring the swallowing of different tastant solutions preparedin both high and low concentrations.The results confirm thathigh concentrations of the four-taste qualities studied (sweet,sour, salty, and bitter) elicit stronger swallowing pressuresthan lower concentrations. This effect is heightened for saltystimuli and in individuals who are genetic supertasters. Addi-tionally, by exploring both the main and modulatory effectsof perceived taste intensity and palatability on swallowingpressures, this study confirms that perceived taste intensity

influences the effects seen across stimulus concentrationand taste quality in supertasters compared to nontasters.Supertasters report heightened taste intensity experiencecompared to nontasters and therefore show greater intensity-based modulation in swallowing pressures. Additionally,differences in reported palatability for these stimuli wereseen in older versus younger adults as a function of tastequality and stimulus concentration, as well as genetics, andthese differences were carried through to swallowing pressureamplitudes. Specifically, older adults reported greater dislikefor a high intensity sour stimulus than younger participants.Neither taste intensity nor palatability had a direct influenceon the amplitudes of tongue pressure used when swallowingthe test stimuli.

This is not the first time that researchers have exploredvariations in tongue-palate pressure amplitudes during theswallowing of taste stimuli with differing concentrations.Pelletier and Dhanaraj [3] have previously used a similarmethodology and reported that a 0.15M sucrose stimulus and1M salt and citric acid stimuli elicited higher lingual pressureamplitudes compared to water. Their study used a 9-pointhedonic rating scale and showed that while palatability didnot have a direct influence on lingual pressures, incorpora-tion of palatability as a covariate in their model did lessen theeffect of taste quality.

The results of the current study add to the informationpreviously reported by Pelletier and Dhanaraj [3] and arelargely in agreement with our hypotheses. Our study lookedmore closely at the effects of stimulus concentration for sweet,sour, salty, and bitter stimuli without reference to water. Theconcentrations of our stimuli were more extreme in both thelow- and high-concentration directions than those used inthe Pelletier andDhanaraj study [3], with the exception of thehigh-concentration sour stimulus, which was 0.128M in bothstudies. We added considerations of genetic taste status andmeasures of perceived taste intensity andwere able to confirmthat intensity is perceived to be greater for higher concen-trations of taste stimuli and that this difference is noticedmore markedly in supertasters. Further, we confirmed thatpalatability ratings show stronger liking for sweet stimuli thanfor sour, salty, or bitter stimuli and that relative liking ordisliking of a stimulus is dependent on its concentration. Ouruse of the hedonic gLMS scale versus the 9-point hedonicrating scale used by Pelletier andDhanaraj [3] allowed greaterdiscrimination of palatability given its design. With respectto tongue-palate pressure amplitudes seen in swallowing, weconfirmed that higher concentrations of taste stimuli elicitstronger tongue pressures. Consistent with our predictionsand expanding on the young-adult data previously reportedby Pelletier and Dhanaraj [3], no age-group differences wereseen in swallowing pressure amplitudes. A novel findingfrom this study is the fact that high-concentration saltystimuli were rated as having the strongest perceived intensity(regardless of genetic taste group) and elicited the strongesttongue-palate pressure amplitudes in genetic nontasters. Ourprediction that the sour stimuli would facilitate greatertongue pressures than the other stimuli was only true for thesupertaster subgroup (Figure 6). With the exception of thePelletier and Dhanaraj study [3], we are not aware of prior


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Figure 6: Differences in strength-normalized measures of tongue-palate pressure amplitudes as a function of stimulus taste-quality andconcentration in genetic nontasters and supertasters.

studies inwhich both sour and salty stimuli have been studiedtogether, and hence this study opens the door to explorationof taste stimuli beyond sour in terms of the influence of tastequality on swallowing behaviors. Because high concentra-tions of salt can also stimulate a chemesthetic response intrigeminal nerve receptors similar to the response seen withhigh concentrations of citric acid, it is not entirely surprisingto see that increased tongue-palate pressure amplitudes wereobserved with the high-concentration salty stimuli [23, 24].However, it was surprising to see this pattern in geneticnontasters versus supertasters. Nevertheless, it appears thattongue-palate pressure amplitudes increase in response tochemesthetic stimulation. This may have important impli-cations for future studies and also for clinical applications.Our findings provide support for the idea that chemestheticstimuli may elicit improvements in swallowing in someindividuals with dysphagia. Future research will need toexplore thresholds with respect to stimulus concentrationthat are adequate to elicit positive behavioral changes andto determine whether such responses can be achieved withstimuli that remain palatable.

Neither intensity nor palatability ratings were found toindependently influence tongue-palate pressures. Neverthe-less, both of these modulators were found to influence thedegree to which stimulus concentration effects were seen intongue-palate pressure amplitudes. Incorporation of intensityratings into the model revealed an effect by which stimulusconcentration interacted with taste quality and genetic tastestatus, while consideration of palatability led to a main effectof concentration. The combination of observed findings canbe summarized as showing that stronger concentrations oftaste stimuli are rated asmore liked or disliked, depending onthe taste quality, and elicit stronger tongue-palate pressuresin swallowing. Further, supertasters are more sensitive tomanipulations of stimulus concentration. However, it can

also be concluded that the greatest facilitation of strongertongue-palate pressure amplitudes occurred with stimulithat were perceived to have the greatest intensities andelicited a chemesthetic response. The high-concentrationbitter and sweet stimuli, which represented the most extremepalatability ratings, did not facilitate increased tongue-palatepressures.

The findings of this study have important implicationsfor clinicians who are considering the use of taste stimuliin treatment for dysphagia. This study adds to a growingbody of the literature that suggests that the benefits of usingtaste stimuli may depend on whether or not the stimuli havechemesthetic properties. Additionally, our study suggests thatit is relevant to know whether a person is a supertaster ora nontaster and that it may further be helpful to determinethe threshold concentrations of stimuli that are needed toelicit chemesthetic response when choosing stimuli for usein treatment. It is also plausible that some patients withoropharyngeal dysphagia may present with altered sensorythresholds for taste or chemesthesis perception; in thesecases, confirming that a stimulus is perceived to have a hightaste intensitywould be advised before recommending its use.

5.1. Limitations. This study is not without limitations. In par-ticular, the study demonstrates that the high-concentrationstimuli used in the experiment were unpalatable, with theexception of the sweet tastant. This presents obvious chal-lenges in terms of applying the study results to clinical prac-tice. We recommend that the current data be considered as ademonstration of effect, but further researchwill be needed todetermine whether heightened swallowing pressures can beelicited with stimulus concentrations that are more palatable.Furthermore, although the study demonstrates heightenedtongue-palate pressure amplitudes as a function of increased


taste stimulus intensity, it is unknown whether these differ-ences in swallowing pressures can be expected in individ-uals with swallowing impairment and whether they are ofsufficient magnitude to yield clinically relevant differences inswallowing function, such as improved bolus propulsion andclearance.

6. Conclusions

In conclusion, the data show that the perceived intensityof a taste stimulus (which varies as a function of stimulusconcentration, taste quality, participant age, and genetic tastestatus) influences tongue pressure amplitudes in swallowing.Palatability ratings, which vary as a function of stimulusconcentration and differ between stimuli with different tastequalities, do not appear to influence tongue pressure ampli-tudes in swallowing. This finding is consistent with previousresults in the dysphagia literature [3].The high concentrationsour and salty stimuli in this protocol were perceived to havethe highest intensities and elicited the highest amplitudesof tongue-palate pressure. We attribute these findings to thechemesthetic properties of these stimuli.

Conflict of Interests

The authors have no conflict of interests to disclose.

Acknowledgments

Funding for this study was provided through an Ameri-can Speech-Language Hearing Foundation New Investigatoraward to the third author as well as funding from the Uni-versity of Arkansas for Medical Sciences and Johns HopkinsUniversity. The second author acknowledges funding fromthe NIDCD and the Toronto Rehabilitation Institute, Uni-versity Health Network, which supported the contributionsof the first and second authors to paper development. TheToronto Rehabilitation Institute, University Health Network,receives funding from the Provincial Rehabilitation Researchprogram of the Ministry of Health and Long-Term Care.The views expressed do not necessarily reflect those of theMinistry. The authors gratefully acknowledge advice fromKaren Grace-Martin regarding the statistical analyses andfrom Dr. Linda Bartoshuk regarding study design.

References

[1] J. A. Logemann, B. R. Pauloski, L. Colangelo, C. Lazarus,M. Fujiu, and P. J. Kahrilas, “Effects of a sour bolus onoropharyngeal swallowing measures in patients with neuro-genic dysphagia,” Journal of Speech and Hearing Research, vol.38, no. 3, pp. 556–563, 1995.

[2] C. A. Pelletier and H. T. Lawless, “Effect of citric acid and citricacid-sucrosemixtures on swallowing in neurogenic oropharyn-geal dysphagia,” Dysphagia, vol. 18, no. 4, pp. 231–241, 2003.

[3] C. A. Pelletier and G. E. Dhanaraj, “The effect of taste andpalatability on lingual swallowing pressure,” Dysphagia, vol. 21,no. 2, pp. 121–128, 2006.

[4] C. Chee, S. Arshad, S. Singh, S. Mistry, and S. Hamdy, “Theinfluence of chemical gustatory stimuli and oral anaesthesia onhealthy human pharyngeal swallowing,” Chemical Senses, vol.30, no. 5, pp. 393–400, 2005.

[5] P. M. Palmer, T. M. McCulloch, D. Jaffe, and A. T. Neel, “Effectsof a sour bolus on the intramuscular electromyographic (EMG)activity of muscles in the submental region,”Dysphagia, vol. 20,no. 3, pp. 210–217, 2005.

[6] C. M. Steele, P. H. van Lieshout, and C. A. Pelletier, “The influ-ence of stimulus taste and chemesthesis on tongue movementtiming in swallowing,” Journal of Speech, Language, andHearingResearch, vol. 55, no. 1, pp. 262–275, 2012.

[7] S. Mistry, J. C. Rothwell, D. G. Thompson, and S. Hamdy,“Modulation of human cortical swallowing motor pathwaysafter pleasant and aversive taste stimuli,”The American Journalof Physiology—Gastrointestinal and Liver Physiology, vol. 291,no. 4, pp. G666–G671, 2006.

[8] Y. Kajii, T. Shingai, J. I. Kitagawa et al., “Sour taste stimulationfacilitates reflex swallowing from the pharynx and larynx in therat,” Physiology and Behavior, vol. 77, no. 2-3, pp. 321–325, 2002.

[9] A. Majorana, G. Campus, S. Anedda et al., “Developmentand validation of a taste sensitivity test in a group of healthychildren,” European Journal of Paediatric Dentistry, vol. 13, pp.147–150, 2012.

[10] L. M. Bartoshuk, “Comparing sensory experiences acrossindividuals: recent psychophysical advances illuminate geneticvariation in taste perception,”Chemical Senses, vol. 25, no. 4, pp.447–460, 2000.

[11] G. K. Essick, A. Chopra, S. Guest, and F. McGlone, “Lingualtactile acuity, taste perception, and the density and diameter offungiform papillae in female subjects,” Physiology and Behavior,vol. 80, no. 2-3, pp. 289–302, 2003.

[12] A. M. Dietsch, N. P. Solomon, C. M. Steele, and C. A. Pelletier,“The effect of barium on perceptions of taste intensity andpalatability,” Dysphagia, vol. 29, no. 1, pp. 96–108, 2014.

[13] C. A. Pelletier and C.M. Steele, “Influence of the perceived tasteintensity of chemesthetic stimuli on swallowing parametersgiven age and genetic taste differences in healthy adult women,”Journal of Speech, Language and Hearing Research, vol. 57, no. 1,pp. 1–11, 2014.

[14] L. M. Bartoshuk, V. B. Duffy, B. G. Green et al., “Validacross-group comparisons with labeled scales: the gLMS versusmagnitude matching,” Physiology and Behavior, vol. 82, no. 1,pp. 109–114, 2004.

[15] L.M. Bartoshuk, “Genetic and pathological taste variation: whatcan we learn from animal models and human disease?” CibaFoundation symposium, vol. 179, pp. 251–262, 1993.

[16] M. F. Folstein, S. E. Folstein, and P. R. McHugh, “‘Mini-mentalstate’. A practical method for grading the cognitive state ofpatients for the clinician,” Journal of Psychiatric Research, vol.12, pp. 189–198, 1975.

[17] A. Nagy, C. M. Steele, and C. A. Pelletier, “Barium versus non-barium stimuli: differences in taste intensity, chemesthesis andswallowing behavior in healthy adult women,” Journal of SpeechLanguage & Hearing Research, 2013.

[18] L. M. Bartoshuk, V. B. Duffy, J. E. Hayes, H. R. Moskowitz, andD. J. Snyder, “Psychophysics of sweet and fat perception in obe-sity: Problems, solutions and new perspectives,” PhilosophicalTransactions of the Royal Society B: Biological Sciences, vol. 361,no. 1471, pp. 1137–1148, 2006.

[19] C. M. Steele, G. L. Bailey, and S. M. Molfenter, “Tongue pres-sure modulation during swallowing: water versus nectar-thick


liquids,” Journal of Speech, Language, and Hearing Research, vol.53, no. 2, pp. 273–283, 2010.

[20] E. M. Yeates, C. M. Steele, and C. A. Pelletier, “Tongue pressureand submental surface electromyography measures duringnoneffortful and effortful saliva swallows in healthy women,”TheAmerican Journal of Speech-Language Pathology, vol. 19, no.3, pp. 274–281, 2010.

[21] C. Lleras, “Path analysis,” in Encyclopedia of Social Measure-ment, K. K. Leonard, Ed., pp. 25–30, Elsevier, Philadephia, Pa,USA, 2005.

[22] J. W. Kotrlik and H. A. Williams, “The incorporation of effectsize in informaton technology, learning, and performanceresearch,” Information Technology, Learning, and PerformanceJournal, vol. 21, pp. 1–7, 2003.

[23] P. M. Wise and P. A. S. Breslin, “Individual differences in sourand salt sensitivity: detection andquality recognition thresholdsfor citric acid and sodiumchloride,”Chemical Senses, vol. 38, no.4, pp. 333–342, 2013.

[24] C. E. Riera, H. Vogel, S. A. Simon, S. Damak, and J. L.Coutre, “Sensory attributes of complex tasting divalent saltsare mediated by TRPM5 and TRPV1 channels,” Journal ofNeuroscience, vol. 29, no. 8, pp. 2654–2662, 2009.

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